A laser is a device that emits light (electromagnetic radiation) with a high degree of spatial and temporal coherence through a process of optical amplification based on the stimulated emission of photons. The term laser is an acronym for Light Amplification by Stimulated Emission of Radiation.
Components of a laser include an energy supply, a gain medium to amplify light by stimulated emission, and an optical feedback mechanism. A laser generates or amplifies light of a specific wavelengths or a range of wavelengths through the gain medium by converting electrical or optical pump energy into the energy of the coherent laser output. An optical cavity can serve as the optical feedback mechanism. For example, light can be directed back and forth between the two ends of the cavity that act as mirrors, passing through the gain medium while being amplified each time. In some laser designs, one end of the optical cavity (the output coupler) is partially transparent to allow light within specific range of wavelength to escape through.